Problem: Multiply the following complex numbers, marked as blue dots on the graph: $(3 e^{5\pi i / 4}) \cdot ( e^{19\pi i / 12})$ (Your current answer will be plotted in orange.)
Explanation: Multiplying complex numbers in polar forms can be done by multiplying the lengths and adding the angles. The first number ( $3 e^{5\pi i / 4}$ ) has angle $\frac{5}{4}\pi$ and radius $3$ The second number ( $ e^{19\pi i / 12}$ ) has angle $\frac{19}{12}\pi$ and radius $1$ The radius of the result will be $3 \cdot 1$ , which is $3$ The sum of the angles is $\frac{5}{4}\pi + \frac{19}{12}\pi = \frac{17}{6}\pi$ The angle $\frac{17}{6}\pi$ is more than $2 \pi$ . A complex number goes a full circle if its angle is increased by $2 \pi$ , so it goes back to itself. Because of that, angles of complex numbers are convenient to keep between $0$ and $2 \pi$ $\frac{17}{6}\pi - 2 \pi = \frac{5}{6}\pi$ The radius of the result is $3$ and the angle of the result is $\frac{5}{6}\pi$.